1. Field of the Invention
The present invention relates to three-piece railway car trucks, and more particularly, to a method of making bolsters and sideframes for use in such three-piece railway car trucks.
2. Description of the Prior Art
In the past, in making hollow cast metal bodies, it has been known to use cores made of bonded sand supported in green sand molds to produce the hollow castings. The cores have been used to create the hollows or open spaces in the castings.
Cores have commonly been made in core boxes, typically having cope and drag halves that are brought together along a parting line. There is a cavity in the core box, and a mixture of sand and bonding material are introduced into the cavity and cured. The core box cope and drag portions are then parted along the parting line, generally being pulled apart vertically. Because of the need to pull the cope and drag portions apart, the sizes and shapes of the cores to be produced have been limited: the cores have not been able to have parts that would interfere with the movement of the cope portions away from the drag and with removal of the cores from the cope and drag portions. Thus, it typically has been necessary to produce several different cores that are later joined or placed together in the green sand mold.
In the case of cast metal sideframes for railway trucks, many different core shapes have been needed to produce the basic shape of the interior of the sideframes. As shown in FIGS. 15-17, more than twenty cores have been required, with some different cores sometimes adhered together in a separate process step before being placed in a receiving cavity in the mold, and with many different cores and groups of cores separately placed in the mold. While some cores such as a window core and bolster opening cores have been supported on core prints, many of the cores have been supported on chaplets on the mold surface. In addition to the placement of the cores being a labor intensive operation, the use of such multiple cores has been problematic from a quality control standpoint. With so many joints between the faces of the multiple cores, there is a potential for many fins to be formed on the interior of the casting. To remove these fins through a finishing operation has been difficult since the fins are on the interior of the casting. Moreover, these fins create another potential quality control problem since they could give rise to stress risers that could form along the fins. Other potential quality control problems arise from the potential for shifting of the cores"" positions in the mold prior to or during the casting operation. If the cores shift position, the thickness of the walls of the casting could vary from the design.
In addition, multiple cores may be so thin that core rods are required to be used to support the sand. These core rods add to the cost of the process and complicate cleaning of the castings.
Another problem can arise in connection with areas of the sideframe around lightener holes and other openings in the sideframe wall. Metal fins can form around these openings, and sometimes form facing the interior of the casting. To finish such a casting by removing these fins may be difficult to accomplish manually since the fins are less accessible to the worker. In addition, it is very difficult to remove interior fins through automation.
Similar problems have arisen in producing cast metal bolsters for use in railway trucks. Like the sideframes, bolsters have hollow interiors, and have traditionally been made with multiple cores to form the interior walls and interior surfaces of the outer walls. Sixteen separate cores have been used to produce such castings, with cope and drag portions sometimes adhered to each other or juxtaposed along joints, as in the case of the sideframes cores, with chaplets supporting the cores on the mold surface, and with separate cores inserted into the cores to define holes for bolting side bearings and dead lever lugs to the bolster.
Similar problems as those outlined for sideframes have arisen with respect to quality control for bolsters. The positions of the cores on the chaplets may shift in the mold, creating the potential for making a casting with less than or more than desirable wall thicknesses. Bolster production has required that the multiple cores be placed in a mold in a labor intensive operation with multiple joints where stress risers could form. And like the sideframes, interior fins could form around lightener and other openings, fins that could be difficult and labor intensive to remove and that are not conducive to removal through automated finishing operations. Moreover, fins can form on the edges of the openings which can be stressed and damaged during the removal operation in the case of both sideframes and bolsters.
The present invention addresses various aspects of the prior art problems related to the production of cast metal bolsters and sideframes for three-piece railway car trucks.
The present invention provides a method of making a cast metal sideframe for a railway car truck. The sideframe has front and rear ends and pedestals at each end for mounting on wheelsets. The sideframe also has a top member that extends along a longitudinal axis between the front and rear ends. The sideframe has a tension member that has a bottom center portion and a pair of diagonal portions extending from the bottom center portion toward the pedestals. The sideframe has a bolster opening in the middle of the sideframe between the top member and the bottom center portion of the tension member. The sideframe has a vertical column on each side of the bolster opening. The top member has a top surface with a plurality of lightener openings. The sideframe has interior and exterior surfaces. The method comprises the steps of providing a mold having cope and drag mold surfaces, providing a core having a core outer surface for forming at least a part of the interior surface of the cast metal sideframe, placing the core in the mold, and pouring molten metal into the mold to form the cast metal sideframe. In the improved method of the present invention, the core includes at least one core print received in a mating cavity in the mold and a side window portion. The core print is connected to the core outer surface and corresponds in size, shape and position with one lightener opening to be produced in the top wall of the top member of the sideframe. The side window portion and the core print are formed as integral parts of the same core.
In another aspect, a bolster center core has a pair of integral core prints for supporting the core in the mold. The core prints are connected to the core body and correspond with holes in the bolster sidewalls. The prints may, in some embodiments, have stepped surfaces for locating the core with respect to the drag mold. In some additional embodiments, the core print may be used to define part of the bolster center plate or bowl and part of the outside of the casting.
In another aspect, the present invention provides one-piece end cores for the bolster. The two ends of each one-piece end core may support the entire weight of the core in the mold, without support chaplets between the core and the drag mold surface. In some embodiments, the one-piece end core may have integral bolt hole pin cores extending out from the top surface for side bearings.
In another aspect, the present invention provides a method of making a cast metal sideframe for a railway car truck. The sideframe has front and rear ends and pedestals at each end for mounting on wheelsets. The sideframe also has a top member that extends along a longitudinal axis between the front and rear ends. The sideframe has a tension member that has a bottom center portion and a pair of diagonal portions extending from the bottom center portion toward the pedestals. The sideframe has a bolster opening in the middle of the sideframe between the top member and the bottom center portion of the tension member. The sideframe has a vertical column on each side of the bolster opening. The top member has a top surface with a plurality of lightener openings. The sideframe has interior and exterior surfaces. The method comprises the steps of providing a mold having cope and drag mold surfaces, providing a core having a core outer surface for forming at least a part of the interior surface of the cast metal sideframe, placing the core in the mold, and pouring molten metal into the mold to form the cast metal sideframe. In the improved method of the present invention, the core includes at least one core print and a side window portion. The core print is connected to the core outer surface on a diagonal and corresponds in size, shape and position with one lightener opening to be produced in the diagonal portion of the sideframe.